Centralized traffic controlling system for railroads



Feb. 6, 1945. w. D. HAlLEs ET Al.

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed May 11, 19428 Sheets-Sheet 1 FWBrixner,

Feb. 6, 1945. l

F'IG

A Termimng Impedance CENTRALIZED TRAFFIC CONTROLLING SYSTEM FORRAILROADS W. D. HAILES ET AL.

Filed May' 11, 1942 8 Sheets-sheet 2 INVENToRs W.D.Hai\es undFM/.Brixnen THEIR ATTORNEY Feb; 6, 1945. w. D. HAlLEs ET AL 2,368,826

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Feb. 6, 1945. w. D.HAILEs Ef A1. 2,368,826

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed May l1, 19428 Sheets-Sher#l 4 Fl G. 3.A. Control Of'cg 75 1TK 76 c-) 125 q15ML.

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Feb. 6, 1945.

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS See 8Sheets-Shee'kI 7 BY W THEIR ATrEY W. D. HAILES ET AL Filed May l1, 1942Feb. 6, 1945.

CENTRALIZED TRAFFIC CONTRLLING SYSTEM FOR RAILROADS Fl e. 4 B.

INVENToRs W.D.Ha|es and EWBrixner` Feb. 6, 1945. w. D. HAlLEs ErALCENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed May l1, 19428 Sheets-Sheet 8 To NTQL.

Stau +2..: 205 92.55 wzwmmnnw Paiented Feb. 6, 1945 UNITED STATES PATENTOFFICE CENTRALIZED TRAFFIC GNTROLLING SYSTEM FOR RAILROADS.

William, D..v Hales, Brighton, and: Frederick Brxner,A (States,` N. XLIassgnors to General Rail- -way Signal Company, Rochester, N`. Y.

Application May 11,1942, serial No. 442,508

17y Claims.

This invention relates. to; the communication;-

part. of acentralized traiflc controlling System used for governi-rre`tramo on railroads1 and `more.- particularly pertains to a communicationsystem of the carrier currentV codedty-pe.

In, acentralized traffic Qontrol system forrail-` roads, oftenconveniently termed 'l'. sys,-

tem the switches. andsignals at Various.; points along the railroad are:placed undery the control of an operator in a central oice so that,hemay change the position of the switches., subject to automaticapproach and detector locking circuits. which prevent unsafe operationof any switch,

and may hold at stop any of. the signals or allow.

them to clear dependent upon the` position oi their associated switches;and in. accordance with traiiic conditions- A1so such a system provides,means whereby indications arel displayed in, the control ofceto informkthev operator of the4 loca-1 tion of trains on the various tracksections throughout the territory under his supervision, and tovindicate the position and; condition of the various switchesand signals.

Those switches and signals Whichv are, located adjacent each othercomprise what is` con veniently termed afield. Station,l and acornnriuni-t.

cation system is then provided to interconnect the central control,Aoffice with the several field stations for the transmission of controlsto the. iield stations, and for the reception of indications from thefield stations.

In accordance with the present inventiom'it.

selected' frequencies on the line circuit at. the,

control oiiice'for the selection of any desired field, station and thetransmission of controls to that eldlstation. Although, the system ofthe present invention accomplishes this `by the manner in which theapparatus at the control oce and eld stations is inductively coupled tothe line, circuit and also byreason of the use of 'the properfrequencies which-'may `be superimposed upon thev line circuit vWithoutinterferingrv with the transmissionA ofthe other services alreadyemployed oratore.

on the, line circuit, it is to be understood thatthe invention mayjustas-Well be used in connection With a line circuit` free from all'other? types of services. f'

TheA field stationsV must, off course, `bel able toV transmitindications to the control olice and in accordance vvi-th the presentinvention these eld stations are also provided with'v frequency gen-`Each station is vthen provided with: means for superimposing adistinctive series of4 codel impulses of' alternatingl current on thelineA circuit for its own selection and alsov for its registrati'oninvthe control oce as Well as for the'` transmission of' its indicationsafterit has been selected and registered.- For'the` purpose of the ipresent disclosure, the. frequency kgenerators at the eldi stationsare-assumed to `produce the same frequencies as the frequency generatorsat` the control oiiice, and the: description is based on this.organization. Buthk it is to bewunderstood that` diierent frequenciesmight be. employed at` the, field stations (assuming, of' course,properreceiving apparatus is employed at. thev cont-rolfV office.) and stillcome. within the scope of the present: invention.

When afstation is. ready to transmit indications to theA controlottico., it appliesv an initiating.

0r startinerimnulse of alternating current of a particularr frequency tothe line circuit which initiating: impulse prevents all other stationsnot ready t0 begin at that instant trom. thereafter interfering withthe.Series 0f; mllLllSeS that Station is about to tianSinit--` Althouentstart impulse. from the field is or relatively short duration, thecontrol ofce apparatus immediately respondsby placing conditioningimpulse 'Y current, of the same frequency on the line circuit, which.Acurrentv is maintained by the. ofe.

for' the, time, required to` condition `the o'ice, and al1 fieldstationsfor an indication cycle of operatim After the conditioningperiod. that, station which. is ready to transmit indications.: to`diamine trol' cnice, r,Dplies to thedine circuit av series,` of

.code impulses of alternating current, each im:

pulse beine. of.. a Selected frontierscy,4 and, which series'of impulsesforms a code characteristic of that station and includes impulsescharacteristi-icv i of the indications for that station.` When ylie eldstation appliesA an impulse of anyseries to the line circuit,A s uchimpulse is receivedat the control cnice/andan iin-pulse, of thesame,characteristic frequency` is' contemporaneousl'y applied tothe line'circuit atthe `controll binge, Afterv a very short interval7 of time,lthe field station impulse ceases, but thecontrol office applied persistsor continues for a certain additional time during which it iseffectively received at all eld stations and forms what may beconveniently termed a test period. This is done on each succeedingimpulse belonging to the station selection impulses until that stationhas been selected.'

When a plurality of field stations are ready to transmit indications atthe same time, each stadtion applies impulses to the line circuit duringthe station selecting portion of the cycle in ac cordance with itsstation code until it no longer has a chance of being selected. At thecontrol oflce, means is provided in accordance with 'the presentinvention whereby one frequency has superiority or preference over theother, so that those stations which apply an impulse of this superiorfrequency to the line circuit have an impulse of this superior frequencyreturned to them by the control office vwhile the others do not'havetheir inferior frequency returned to them. Thus, those stations applyingor calling for the superior frequency on any given impulse have theirstation selecting means conditioned, while those stations which apply orcall for the inferior frequency drop out and cease transmission untilsome subsequent cycle of operation. This automatic selection by givingone of the frequencies a relative superiority continues throughout thoseimpulses of the series required for station selection and registrationuntil only one station remains on the line circuit which station thenproceeds to transmit impulses characteristic of its indications. Inbrief, the station selection for the transmission of indications isaccomplished on a code superiority basis with the relative superioritybetween the diierent code elements being selectively determined at thecontrol office. This principle of selection is employed so as toincrease the integrity or reliability of such a system, and

particularly for the purpose of solving certain problems inherent in asystem employing different frequencies superimposed on a line circuit.For example,-if the system were of the type where it is necessary thatan inferior field station receive the superior frequency as transmittedfrom the superior field station, -it is entirely possible that theinferior eld station might fail to detect the presence of the superiorfrequency because of phase cancellation due to conflict between thetransmitters of two superior field stations. Under such conditions, theinferior station which failed to receive the superior frequency wouldnot be cancelled or drop out; and would continue to transmit althoughits code might be inferior to the codes transmitted from the other twostations and which would thus cause erroneous indications to beregistered in the control office. I'his particular problem is solved bythe present invention inasmuch as the field stationsA can always hearthe control office, so to speak, although they may not always be able tohear each other.

. In other words, the retransmission of each impulse from the controloffice in response to a, corresponding impulse received from the eldstations, makes it possible to organize a system in which the problem ofphase cancellation is avoided by providing a short interval of time near.the close of each impulse of the code during which the control ocetransmitter is the only trans-` mitter onV the line circuit, togetherwith a eld station selecting equipment which requires that theretransmitted impulse must be received by the field station during thisshort interval of time at the close of such impulse (conveniently termedtest period) in order for that station to be selected.

Another object of the present invention is to provide a coded typesystem which will minimize the effects of the cross-fire between thedifferent frequencies on the line responsive relay In a carrier currenttype of communication system, lters and amplifiers must be provided torespond to certain frequency bands, but, with these frequenciesreasonably close together, the application of onevfrequency may cause atransient condition vwhich simulates the other frequency therebyinterfering with the line responsive relay means for such otherfrequency. The present invention minimizes this possibility by providingsuitable selectingr vcircuits which need function only during testperiods when the control office transmitter is the only transmitter onthe line and transients have subsided.

In a system of this character, it is necessary to have the transmittersand receivers at the eld stations vset with the proper gains to insurethat each field station will transmit at an energy level suiciently highto be received at the control ofce and to insure thatthe impulsestransmitted by the control ofce will be properly received at the eldstations. For example, this means that a distant iield station receivermust be set at a high gain in order to properly receive the impulsestransmitted from the control office at the otherl end of the line, andit also means that the output energy level of the transmitter at suchdistant field station must be high in order to be received by thecontrol` oice. This combination of a receiver of high gain at the sameor an adjoining location with a transmitter of a high output levelincreases the tendency of one frequency to cross-fire into theother'frequency at that receiver. This source of potential difficultydue to cross-fire between frequencies, is overcome by the "feature ofthe present invention employing retransmission of each impulse by thecontrol olce, the latter part of whichfforms a test period during whichthe control oiiice transmitter is the only transmitter on the linecircuit, because it is obvious that with but a single frequency on theline circuit, there is no possibility of cross-rei conditions. l

Another advantage of a system organized in accordance with thisinvention is the manner in which the output levels of eld transmittersmay be adjusted in accordance with their geographic relationship to thecontrol office so that code impulses received from the various fieldstations are received with substantially the same intensity or energylevel at the control office. 'I'his is particularly advantageous when itis remembered that the control ofiice receiver must be adjusted withsufficient amplifying gain to properly re. ceive impulses transmittedfrom the most distant ofthe frequency characteristic of any impulseascaaae cations', and is: arranged. so that. if there is ,al n

since the. control office receivermust be set at such again as to mostprofltably receive the most distant transmitter on the line. circuit.However, by employing the feature of retransmission in a systemorganized in accordance -with the present invention, this diculty fromcross-fire at the control oice is eliminated Without additional costand` complication.

Another object of the present invention is to provide a system in whicha field station is retired (or fails to be selected) when it'has adefective synchr'onizing or locking-in type so that if two fieldstations start transmission at the same time v these generators willoperate in phase for each of theV impulses transmitted from suchstations. Each ofthese arrangements of generators provides distinctiveproblems and characteristics in connection with the line circuits, butthe object of the present invention is to provide localv con.. trolcircuits for the control cnice and the iield stations which will beoperative Witheitherr ar-v rangement.

Another object of this-invention is to provide a simplex type ofcommunication system, that is, a system in which only controls orindications can be transmitted on'any particularcycle of operation eventhough the control oflice and eld stations have separate sources ofenergy and can initiatexa cycle of operation at any-timewhile the systemis at rest.' This feature is accomplished by arranging that theinitiating or conditioning impulse applied at the control oflice, asabove mentioned, is of one frequency if acontrol'oilce start occurs toinitiate a cycle ofoperation' for the transmission of controls, but suchinitiating or conditioning impulse is of a different vfrequency if afield station initiates a cycle-of oper ation for the transmission ofindications. At` the end of a cycle of operation,the control ofceapplies a permission impulse on the line which is of the same frequency`as applied for a field station start impulse, and this permissionimpulse places the eld station incondition to initiate an indicationcycle of operation,`but when the control oiiice has new `controls totransmit to a eld station, this permission impulseis not applied to theline bythe control oflice, so that the following cycle `of operation isfor the transmission of controls. The field stations, although ready totransmit, cannot elect a eld station start until the control office hascompleted the transmission of the new controls and places the temporarypermission impulse on 'the line.

Another object of the linvention is to provide a system in which theindication cycles will be distributed between the different eld stationshaving'indications to transmitso that if `any particular station has alarge number of indications to transmity because of frequent changesyin' indication conditions at that station it cannot dominate the system.In other words, the*V system provides what isl `conveniently termedgroup of viield stations ready to transmit attire same timeyeach ofthese stations has. an oppor-` tunity to transmit only one cycle ofoperationun'- til all of the stations in that group have transmitted.Atthe .end ofthe transmission of the successive cycles of operation bythis' group ofV stations, a prolonged period of rest occurs during whichall stations then having indications ready to transmit form anothergroup, so as` to speak, and indications are then transmitted onsuccessive cycles of operation from such another group of stations. lOther objects, purposes, and characteristic features of the presentinvention will be in .part obvious from the accompanying drawings andinpart pointed out as the description of thehinvention progresses.

In describing the invention in detail, 'reference will bemade to theaccompanying drawings, in which those parts having similanfeatures andfunctions are designated throughout the several figures by like letterreference characters which are generallymade distinctive either byreason of preceding numerals representative of their location or byreason of succeeding numerals or, exponents representative of the orderof their operation, and in whichf Y Fig. 1: illustrates in adiagrammatic manner the relationship oftthe C. T. C. system of thepresent invention to the various other services which may be associated.with aline circuit upon which the` system` of the present invention maybe superimposed;

Figs. 2A and 2B when placed end to endillusz trate diagrammatically theline circuitarrange: ment of the present invention whenv applied to aline circuit having no other services thereon as well as showing theinterconnections betweenthe line circuit and the control apparatus inthe control ofiice and at a typical one of the lieldstations;

Figs. 3A and 3B when placed side byside il.. lustrate `the apparatus andcircuit arrangementv employed at the control cnice;

Figs. 4A and 4B when placed side by sideillus.- trate the apparatus andcircuitsemployed at a typical eld station `arranged and controlled inaccordance with the present invention;` and.,

parts and circuits constituting the embodiment-l or theY invention havebeen shown diagrammatically and certain conventional illustrations havebeen employed; the drawings have been `made more with the purposel offacilitating the disclosure` as' to the` principles and mode ofoperation than With the idea of illustrating the specific constructionand arrangement of parts that would be employed in practice. Thus, thevarious relays and their contacts are illustrated in a conventionalmannenand symbols are used to indicate the connections to Ythe terminalsobatteries' or other` vsources ofV electric current lnsteadof' bring"-`ingall of the wiring connections to those termina1s Y The symbols andare employed to indicate the positive and negative terminalsrespectively of suitable batteries or other sources of di. rect current;and the circuits withv which these symbols are used. always have currentowing in the same direction. The symbols' (B+) and (B) indicateconnections to the opposite terminalsof a suitable battery or otherdirect current source which has a central tap or intermediate tapdesignated (CN) and the circuits with which these symbols are used mayhave current owing in one direction or the other depending upon theparticular terminal used in combination with the intermediate tap (CN).Whenalternating current is used in place of direct current, theparticular symbols employed should be considered to represent therelative instantaneous vpolarities.

GENERAL ORGANIZATION C. T. C. SYSTEM SUrimIMPosEDk oN LINE CIRcUIrHAVING OTHER SERVICES `With reference to Fig. 1 of the accompanyingdrawings, a line circuit having line wires l0 and II is shown extendingbetween two repeat coils I6 and I1. Connected across Athe line wires ofthis line circuit is a dispatchers telephone equipment graph linecircuit. Similarly, one purpose of the repeat coil I1 is to terminatethe telegraph line circuit and still permit the telephone frequenciesand the frequencies of the centralized traiic controlling communicationsystem to be repeated in the usual way. If the centralized traflccontrol is to be terminated at this point, it is to be un-` derstoodthat suitable termination impedances must be associated with orincorporated into the coil Il. The features of proper line termination,v

of course, have nothing to do with the present invention and should beaccomplished in the usuali well known manner.

The control'omce selective ringing equipment effects the transmission ofimpulses over the line` circuit at the rate of about 3'1/2 cycles persecond in a manner to form different number codes.V Thev telephoneselector for each station is responsive to only the code assigned to itstelephone station.

When a telephone station is selected, its bell is caused .to ring untila stop ringing pulse is transmitted by the selective telephone ringingequipment. The operator at the telephone called will then communicatewith the dispatcher by voice'. It may be noted Athat the dispatcher isalways listening and will hear any telepho-ne without bel ing called 4byringing. If someone at one tele-v phone station desires to communicatewith someone at another telephone station, he merely asks the dispatcherto call such another telephone station.

It is, of course, understood that the telephone voicefrequencies mayhave a very wide range, but for allpracticalvoice conversations a rangeof frequencies between 200 and 2500 cycles is all that is required. TheVcontrol oice equipment and -the eld station equipment for .thecentralized traic controlling (C. T. C.) system are connected inmultiple across the line circuit through suitable coupling units andlters which, are designed to pass only the frequencies desired for theoperation of the C. T.C. system, whereas the low-pass lters for thetelephone equipment are arranged to pass only the frequencies requiredfor voice transmission, namely 200 to 2500 cycles. For the purpose ofthe present disclosure, the frequencies selected for the C. T.V C.system are 3300 In systems of this character where various fre` quenciesare to be imposed upon the line circuit,l it isdesirable to properlyterminatethe line cir.-

cuits so as to prevent the reflection of the, alternating currents whentheyfreach the end of the line. For example, assuming that the linecircuits are improperly terminated, the application of an alternatingVcurrent potential at one end of the line circuit results in the rotationof the vector or phase relationship in Aone direction as this potentialis taken from the line circuit at successive points away from thecontrol oi-ce, and with the line circuit improperly terminated, suchalternating current potential is reected bythe improper condition at'theend of the line so as to produce potentials which in eiect originate atsuch end of the line and which flow toward the originalend of the linewith the phase relationship rotating in an opposite direction. Thisproduces nodes and anti-nodes at various points along the line circuit.Thus, if a C. T. C. field station equipment were located at a pointalong the line circuit at which a node occurs in this improperlyterminated line circuit, such eld sta-r tion would not receivesignalling current. .Howeven such undesired end of line reflections.would noto-cour if the line circui-t were of an infinite length or wereproperly terminated by the placing of impedances Aacross the ends of theline equal to the natural surge impedance of such line circuit; l Thus,it is desirable that suitable terminal impedlances be placed at the endsof the line circuit used for the C. T. C. system. With` be properlyterminated with respect to the C. T. C. f

portion ofthe line circuit.

, C. T. C. SYSTEM ALONE oN LrNE CIRcUrr In Figs. 2A and 2B, a unecircuit having uve wires I2 and I3 is shown for a C. T. C. systemprovided in accordance with the present invention kin `which there areno other services on the line circuit.` These line wires I2 and I3provide a line circuit which, Yof course, must have similarcharacteristics asA the one disclosed in connection with Fig. vf1, thatis, itv must 'beproperly terminated so as to prevent reflection from Ythe ends of the line.. Tjhus, terminatingimpede.y ances- I andV` I 9 areprovided; at theV opposite ends of the line to properly terminate theline circuits `each having an impedance equal to the natural surgeimpedance of an innnitely long line havthis connection, it shouldbenoted that the present invention can also be applied to a commerl cialpower distribution system .providingalternating current of the usual 60cycle type. Such an application of the present invention is particularlyadvantageous in view of the usual organization of signallingv systemsfor..railroads in which the field locations are provided with storagebatteries having a 60 cycle alternating cur.- rent trickle chargeapparatus vassociatedtl'ierewith. Thus, the system ofthe presentinvention could be applied to such a railroad signal- .ling systemwithout the installation vo1 added line wires. When the system.issuperimposed on a power network or line circuit, it is necessary toprovide blocking impedances at power: connections to such line circuitin order to prevent .the escape o-r attenuation of the carrierfrequencies. Also, the ends of such power line .circuit would, ofcourse, necessarily have tor be provided with terminating impedances inthe usual way.

In Figs, 2A and 2B, the line circuit is shown as having a control officeat one end and several field stations spaced at intervals along the linecircuit toward the other end, but it is to be understood that the systemmight be arranged to have the control cnice at some intermediate pointwith respect to the eld stations.

Each field station equipment as well as the control office equipment isconnected to the line wires l2 and I3 through condensers 20 and `2lwhich `have a suitable insulation strength to protect the C. T. C.4equipment from high voltages.

Each field station and the `control oiiice` includes code transmittingand receiving apparatus. This transmitting` apparatus for the controlofce or any field station comprises selector apparatus, frequencygeneratingr apparatus and the filters required to impress the potentialon the line circuit; while the receiving apparatus comprises lters andamplifiers for receiving impulses over the line circuit and directingthe impulses of the different frequencies to the proper line relayresponsive means which in turn act upon the selector apparatus.

The transmitting apparatus for the control office and any eld stationhas two frequency generators designated respectively f1-Gen. and f2-Gen.which are controlled by the selector apparatus in the control ofceor atthe field station as the case may be to impressy alternating ner and.filter units are arrangedk to provide such relay means F1 and F2 withenergy to pick up their contacts only when their respective frequencies3300 and 3500 are impressed upon the line circuit. .It is, ofcourse,understood that these amplifier and filter units will pass ia. certainband of frequencies at 3300A and 3500 respectively and also thattheseparticularfrequencies have been chosen as examples of frequenciesv whichdo not interfere with the telephone equipment illustrated in Fig. 1 andalso which dor not interfere with radio receiving sets adjacent the linecircuit of either Fig. 1 or Figs. 2A and 2B. Detail consideration willnot be given in this application to the amplifier and filter arrangementfor'the receiving units., as they'may. be ofv any suitable type known inthe art. Similarly, the coupling units may be -of yany suitable typeoperable with the particular types of generators and receivers used,

Withl reference 'to Figs. 2A and 2B, itv will be seen that the frequencygenerators, amplifier and filter units, and coupling `units receivingthe tWo different frequencies havebeen shown diagrammatically for thecontrol omce and for field station No.1 and the connections totheseunits eX- tend to dotted rectangles. The selector apparatus for thecontrol office is shown in Figs. 3A and 8B while the selector apparatusfor field station No. l is shown in detail in Figs. 4A and 4B asdesignated in the drawings. It will be noted that field stations No. 2and No. 3 have current impulses on the line circuit through a tion andcontrol office are provided `with two lineresponsive relay meansdesignated F1 and 1"2 which are respectively .connected to their re'-spective amplier and lter units to vthe line Wires I2 and I3 through iacoupling unit and condensers 20 and 2l. VTheir lrespective amplimerelybeen designatedv by rectangles bearing .thelegend receiving andtransmitting'appal as the description progresses.

CONTROL OFFICE APPARATUS v With reference to-Figs. 3A and 3B placed sideto side, it will be seen that the line responsive peat each of theimpulses impressedy on the line circuit as repeated `by the line relays.F1 and F2 except in the case ofthe permission pulse.- The usual cycledemarking relays SA, SB and SC, all of the slow-acting type, areassociatediwith the line repeating relay FA. Two line condition relays Land R areprovided to bevresponsive to the permission impulse at theendof a cycle of operation which permission vimpulse occurs only if thecontrol cnice has no morevcontrols to `transmit and the line circuit maybe employed on a successive cycle Aof a field station for transmittingindications. Inuthis connection; two starting relays C-jand CF areprovided. TherelayC y is responsive to manual actuation of start buttonsfor starting a cycle of operation for the transmission of controls andthe relay CF is responsive to a start 'pulse automatically applied at afield station for` starting a cycle of operation for the transmissionofindications.

The above mentioned relays together with an impulsing relay E and itsrepeater EP cause the operation'of the stepping relay bank including`stepping relays V and a half-step relayVP. i

The control panel has mounted thereon the various control levers, startbuttons, indicator lamps and the like, as well as the usual miniaturetrack diagram. Each eld station has its group of control levers and astart button B. But for the sake of .simplicity only the switch controllever I SML for the switch machine ISM at the field station No. 1, hasbeen shown with an associated start button IB;

A cancel button CNB is located on the panel and is rendered effectivewhen actuated, to cancel the transmission of any new controls that havebeen set up by the operator.

When a start button B'is manually actuated, it causes the .picking up ofits corresponding change relay CI-I which in turn acts upon itsassociated code determining relay LC if the system is then in conditionfor transmitting control code.

xThis `relay LC acts throughv an associated LCS relay to energize thecontrol starting relay C.

The control starting relay then causes the trans-` mitter relays T1 and'I'2 to be rendered effective to transmit 'the station code and controlsto the desired station. Relay T1 when energized causes frequencygenerator f1-Gen. to be effective to impress 3300 cycle current on theline circuit, while relay T2 when energized causes frequency ,generatorf2-Gen. to be effective to impress 3500 cycle current on the linecircuit.

A slow-acting relay OC is provided to cause the system to go into aperiod of rest if for some stations.

The li'ne responsive relay means. includes the line relays IFl'and IF2.The line repeating relay IFA is associated with these line relaysforrepeating each of the impulses of a series of impulses which areimpressed upon the Vline circuit. However, relay vIFA does not respondto the permission pulse. Cycle demarking relays SA and SB are alsoprovided.

The line condition relays IL and IR are provided at the eld ystation andare conditioned to render the eld station elective to transmit only if apermission impulse is placed upon the line circuit following any seriesof impulses which permission impulses advises each of the field stationsand the control office that the system, a1- though at rest, may beinitiated into operation for the transmission of indications as well asthe transmission of controls. It is through the functioning of theserelays and their associated circuits that the control oce is madesuperior or dominant over the field stations so that an operator maytransmit controls on successive control cycles to any number of eldstations irrespective of the fact that indications may bel standingready at various field stations awaiting transmission. The linerepeating relay IFA causes the operation of a stepping relay 4bankreason the system should fail to properly operate and cause anindenitely prolonged impulse to be placed upon the line circuit.

Through the line repeating relay FA and suitable circuit connections tWorelays TON and LON are provided to time the length of the on or impulseintervals during `the transmission of indications so as to .properlycontrol the indication receiving relays, such as ITKR, in accordancewith the length of the impulses as well as in accordance with thedistinctive frequencies of such impulses.

'Ihe station registration relays RF are controlled in accordance withthe station selecting code so as to cause the energization of thestation relay ST for the particular station then selected to render theindication relays for that station responsive to the character of theimpulses received over the line circuit for the remaining impulses ofthat indication cycle of operation. The relay ITKR is an indicationrelay of the twoposition magnetic-stick type and is associated in thisdisclosure with the condition of track occupancy at station No. l. Whenits contact 22 -is positioned to the left, it energizes lamp ITK toindicate that a train is on the associated track section at station No.l.v It might be noted in thisconnection that theregistration relays RFare provided, one for each impulse of the station;

selecting and registration portionvof a code, while there is a relay STprovided for each of the field stations. `It is, of course, understoodthat these relays are controlled through suitable selections which aremade in accordance with the regular well-known Baudot code as shown inthev prior Patent No. 2,259,561, dated October 21,1941, granted toHailes and Brixner.

FIELD STATION APPARATUS including steppingrelays V and a laststep relayILV as well as a half-step relay IVP.

The operation of thesystem during* the trans-,

mission of a control code effects the selection of the station throughthe proper control of the station selecting relay ISO and its repeatingrelay ISOS, 'but during the transmission 'of the impulses for anindication cycle of operation the station vis selected for transmittingindication impulses by the proper control of the relay SI and at thesame time i's registered in the control office on the registering relaysRF. and station lrelay ST.

The transmission of a control to the field station after its selectionactuates a suitable relay means to a proper position for controlling anydesired traic controlling device which has been typically illustrated inthe control of the relay ISMR whichin turn controls the switch machineofproper frequencies to ,select that field station Y and register itsindications in the control oiiice. An impulsing relay IE is provided tocause the proper timing of the relays. Associated with this apparatus isa transmitting timer relay ITC and its repeating relay ITCP. Relay ILONis provided to time the long impulses impressed by the line circuit bythe field station. It isf of course, understood that the transmittingrelay IT1 and I'I2 control the frequency generators at the eld stationin accordance with the code to be transmitted as indicated in Fig. 2B.

It is, of course, understood that various other auxiliary devices andcircuits therefor will be employed in a C. T. C. system embodying theOPERATION The communication system provided by the present invention isnormally at rest. When the system is applied to the line circuitarrangement of Fig. 1, it is normally deenergized so far as the C. T. C.communication system is concerned, but it is to be understood Athat theother vservices may be employing the line circuit. In Figs. 2A

and 2B where the C. T. C. communication system is the only service onthe 'line circuit, it is, of course, obvious that the line circuit isde'energized unless the C. T. C communication system is in operation.

Any iield station or the control office can initiate the system intooperation to transmit new indications or controls respectively. Ifseveral field stations are ready for transmission atthe same time, theyare transmitted from such`fle1d stations to the control office one cycle=for each field station until each of those stations have ob- NORMALCONDITIONS While the system is at rest most of the relays and circuitsare deenergized, and are `thus organized to save energy while the system`is not in operation. However, the line condition relays L and R. at thecontol oflice and at the field stations lare normally energized.

With reference to Fig. 3B, it will be seen that the relays R and L areenergized in series from (-1-), through a circuit including back`contact 3.0 of relay SB, winding of relay L, front contact 3I, windingof relay R, to This stick circuit can, of course, be broken only by thepicking up of contact 3U of relay SB, in which case the relays R and Lboth drop away.

When these relays are dropped away and the back contact 30 of relay SBis again closed, the relay R can only be picked up by an energizingcircuit closed from (-I-) and including vback contact 30 of relay SB,back contact 32` of relay L, front contact 33 of relay F2, winding ofrelay R, to It will be noted that the picking up of the relay R closesits front contact 3I, but the relay L canot pick up to open its backcontact 32 so long as the iront contact 33 of relayF2 is closed therebyproviding a shunt circuit across both terminals oi the relay L. However,when the front contact 33 of relay F2 isopen, at the end of a permissionpulse as will be hereinafter described, the relay L then picks upinseries with v the relay R and is vmaintained energizedthrough thestick circuit above traced.

With reference to Fig. l4A, 'a similar energizing stick, circuit isnormally closed for the relays IR and IL from through a circuitincluding back contact 34 of relay ISB, wind-ings of relay IL, frontContact 31 of relay IR., windings of relay IR, to When relay ISB ispicked up, both relays IR and IL are released, but may be again pickedup when relay ISB is again released. The pick-up circuit for the relayIR is provided from (-I-l through a circuit including back contact 34 ofrelay ISB, back contact 35of relay IL, front contact 36 of relay IF2,windings of reiay IR, to IL is, of course, the same as the stick circuitabove traced, but with the. pick-up circuit for the relay IR open atfront'contactv 36 of relay 'I'he change relay ICH (see Fig. 4B) is alsonormally energized from (-1-) through a circuit `including front contact21 ofrelay IT, front contact 38 of relay` IM, front contact 39 of relayICH, lower winding of relay ICI-I, to It is, of course, understood thatthe track relay IT ,is normally energized by a track circuit` not shownin detail, and the signals at stop relay IM is also normally `energizedby circuits not shown. Al-

though .these relays IT and IM are shown normally energized with thesystem at rest. it is to be understood'that either or both may bedeenergized and the `system still remain at rest, the indicationsassociated therewith having been transmitted on some operating cycle andcaused the restoration of the Vchange relay ICH to a picked-up positionin which itis also maintained energized through its stick circuitthrough either front or back contacts 21 or front or back conf tacts 38until anotherfchange in condition occurs.

MANUAL START At any time that the operator desires to transmit controlsto a particular station, he first `positions the control'levers forthatstation and then actuates momentarily the start button B associatedtherewith.

The arrangementof the circuits for thelcontrol of the associated relaysCHI, ILC, and LCSis vsuch as to provide that only one eld stationmayVhave controls i transmitted thereto at .any one time, but these relaysand associated circuits are also eiective to store a manual start forany one or several `'leld stations until the system is available for thetransmission of controls to those stations. 'I'his is necessary eventhough the system is arranged to make the control ofce superior to theiield stations, because at the time the operator actuates a start buttonB the systemv may be transmitting indicationsfirom some iield station ormay be transmitting `controls to `some other field station. Thepredetermined order in which the controls are transmitted tothe'different field stations when the operator actuates several startbuttons B'in quick succession is determined by the interlock between thevarious CH y and LC relays of the interlocked bank as shown 'of cancelbutton CNB, to

and described in our above-*mentioned Patent No.. 2,259,561.

Let us assume that the operator desires tok transmit controls to eldstation No. 1 and properly positions the control levers for that stationlto the desired positions, such as lever ISML, for

It will, of course; be apparent that the start buttonvIB need beactuated only momentarily by the operator, because the relay CHI ismaintained energized by its stick circuit as soon as its front contactMis closed.

If the system is at rest, the picking up of the relay CHI closes lanenergizing circuit for the The pick-up circuitr for the Vrelay of relaySB, back contact 45 of relay LCS, back contact 4'! of relay CF, wire 48,back contact 49. of relay CH2, front contact 50 of relay CHI, upperwinding of relay ILC, bus wire 5I, front contact Y 42 of cancel buttonCNB 'to It will, of course, be noted that if the system is in operation,the relay SB will be energized and the back contact 45 will be opened sothat the relay ILC could not be picked up. Also, the system may havebeen just initiated' by some other start button-B or by some change inconditions at the eld station causing the pick up of either the relayLCS or the relay CF opening either contact 46 or 41 respectively as willbe presently pointed out. However, assuming that the system is at rest,the relay ILC picks up closing a stick circuit from through a circuitincluding back'contact 52 of relay SB, winding of relay LCS, wire 53,front contact 54, lower winding of relay ILC, bus' wire 5I, frontcontact 42 of cancel button It will be noted that the relay LCS is inseries with this stick circuit for the relay LC and as soon as it picksup, it opens its back contact 4B and prevents all other ,LC relays frombeing picked up. Also, energy (-1-) is applied to the right handterminal of relay LCS by back contacts SI and |50 of relays C and V4respectively in'multiple with back contact 52 of relay SB for reasons4later pointed out. i

Both the bus wires 4I and 5I are connected t negative potential throughnormally closed front contact 42 of cancel button CNB, so that if at anytime a start button B is actuatedprematurely or inadvisedly theAoperator can immediately cancel such storage of a start condition by theactuation of the cancel button CNB opening front contact 42 and therebydeenergizing any relay CH or LC then picked up.

As so-on as the relay ILC picks up and is energized through its stickvcircuit also energizing the relay LCS to initiate the system intooperation, the back contact 43 of relayILC is opened to deenergize therelay CHI so that it drops away.

It will be seen that the pick-up circuit for the relay ILC includes backcontact 49 of relay CH2 so that if both the buttons IB and 2B wereactuated simultaneously, the relay 2LC would pick up in preference tothe relay ILC, but the relay CHI would remain stuck up so that after anoperating cycle had occurred .for the'transmission of controls to thefield station No. 2 corresponding to the relay 2LC, 'the relay CHI wouldthen be effective to pick up its associated relay ILC, because at suchtime the relay 2CH would be dropped away. Under the circumstances,assumed above, where the -button IB has been actuated and the relay ILCpicked up, then the actuation of the start button 2B merely causes theenergization of relay H which is stored until the transmission ofcontrols has been eiected for the station No. 1.

The picking up oi the relay LCS closes a p ickup circuit for the controloffice starting relay C from (-|r-) ,throughacircuit including backcontact 55 of relay SB, back contact 56 of relay F2, front contact 5'!of relay LCS, back contact 58 of relay CF, windings of relay C, to Assoon as the relay C picksup,itsstickcircuit is c1'osedfrom(-{-)1,through a circuit including front contact 59 of relay LCS, front contact60 of relay C, windings of relay C, to Another stick circuit is alsoclosed for the relay C from (-|-),.through a circuit including backcontact 6I of relay SC, front contact 62 of relay C, windingsof relay C,to The picking up of the control ofce start relay `C opens its backcontact 62 included in the stick circuit of the field start relay CF.This gives the control oce start relay C the priority .in the event boththe relays C and CF are energized LV, back contact 61 of relay V4, backcontactV -68 of relay V3, backl conta-ct 89 of relay V2, back Contact I0of relay V1, to the bus Wire 'I5 which extends to the relay T1, windingsof relay T1, to l The picking up of the contacts of the transmitterrelay T1 closes its front contact 'I1 (see Fig. 2A) for completing anobvious energizing circuit for the frequency Vgenerator f1-Gen. which inturn impresses the frequency f1 on the line circuit to condition andinitiate the apparatus at the control office and each of the eldstations for a control cycle of operation. This conditioning impulse isindicated as the iirst impulse of a cycle in the chart of Fig. 5Ashowing a typical control cycle.

As heretofore mentioned, this frequency f1 is always impressed on theline circuit for the conditioning impulse of a control cycle and thelength of this conditioning impulse is determined by the sequence ofcertain relays immediately following the picking up of the relay C.

More specifically, the picking up of the relay C also closes a pick-upcircuit for the relay OC from through a circuit including back contact80 vof relay SC, front contact 8l of relay C, f

back contact 82 of relay CF, windings of relay OC, to The relay OC is,of course, slow acting but it picks up after a short time to close itsfront contact 83 in readiness to complete ay stick circuit and also tosupply energy to the impulsing circuits for the transmitter relays T1and T2 during the operating cycle being initiated.

At the control ofce, the line responsive relay F1 responds to thefrequency `f1 of the conditioning impulse and closes its front contacts.'Ihis completes an energizing 'circuit for the line repeating relay FA.from through a circuit including front, contact 84 of relay F1,windings of relay FA, t0

The picking up of the relay FA closes its front contact 85 to completean obvious energizing circuit for the relay SA; the relay SA in turncloses it's front conta-ct 86 to-complete an obvious energizing circuitfor the relayv SB; and the relay SB in vturn closes its front contact 8lto/ complete an obvious energizing circuit for the relay SC. Thus, it'will be seen that the relays FA, SA, SB and SC' pick up in sequence.

The picking up of the relay SC opens the pickup circuit for the relay OCat back contact 8l), but prepares a stick circiut for the relay OC atfront contact 83 which is closed at the termination of the conditioningimpulse and during each succeeding impulse. This stick circuit for thevrelay OC is closed from through a, circuit including front contact 83 ofthe relay OC, front contact 88 of the relay SC, back contact 89 of therelay F1, back conta-ct 90 of the relay F2, windings of the relay OC, toIt is noted, howaccesso ever, that this sticklcircuit is `nosed onlyduring Also, if lthe conditioning impulse should be maintained for anunusual `length of time, the stick circuit would be open at vbackcontacts 89 and 90 and the relay C would be dropped away.

At the time the relay .C picks up, an energizing circiut is closed forthe relay E from through a .circuit including-atront contact 9| of therelayC, wire 92, .back contact .93 .of relaylLV, back ,contact 94 `ofrelay V4, .back `contact195 of relay back contact Shot-relay'V?,.backcoutact 295| of .relay V1, Aback .contact .198 Aof relay Wire.9:9., windings of relay E, .to

'l'.fl'ie picking-.up of therelay Eicloses yits .front contact |^01| .sothat upon 'the picking lupof'the relay ySB .and prior to thepick-ing upof the relay. SC opening back .contact 88 -an .energizing circuit isclosed .for the transmitting relay T1, from through a circuit includingfront contact 83 .of relay IOC, front contact 0.2 fof relay SB, `frontcontact .|0| of relay E, lfrontcontact 64 of relay C, wire y65', backcontact`r 66 of relay LV, llaack'contact B1 of relay V4, back contact 68`ci relayV3, back .contact .59 lof relay V2; back-contact 10 of relayV11, .tothe bus wire .15; and thence .through OPER-Arron or" STEPPINGRELAY BANK AT' THE CONTROL OFFICE l The .stepping relay` bank-at the`.control office comprises a series ofY stepping 4relays V, la' laststepping relay LV and a. half-step relay These stepping relays aresuccessively picked up on each off period of Vany series of impulses,while the half-step relay VP assumes anv opposite position foreach onperiod of the Asame series. T-he first operation of the stepping .relaybank thatoccurs subsequent to the YactuationI of a start button for thetransmission of controlsis the picking up -o the half-step -relay VPduring the conditioning impulse following the picking up of theslowacting relay SC. These sequential operations of the relays V and VP areindicated inthe chart of Fig. 5A where the arrows pointing up and downrespectivelyindicate the'pcking. up or 'dropping away vof areassociated. y v

The pick-up `circuit .for the relay VP is closed. from through a circuitincluding front contact y45 `of relaygSB. front contact 03 of relaySC,`fro-nt Contact |04 of relay FA, fwire |05, backv contact IDS -ofrelayLV; back Contact .I 01 of vrelay V4, back contact +08 of relay'Vf,back contact |09 the relaysfwith which they4 of relay V2, back contact'H0 Y*of relay V1, windings of' relay VP, to As'soon `as "the relay VPpicks up, the stick circuit is completed therefor from "(+9 through acircuitl including front contact I|5of relay/SB, front contact |03 ofrelay SC, wirel I, front contact ||2 of relay VP, back contact |06 ofrelay LV, back contact |01y of relay V4, back contact |08 vof relay V3,back contact |09 'of relay V2, back contact H0 of relay V1, windings ofrelay VP, to This stick rcircuit is maintained closed until the iirststepping relay of the bank is vpicked yup which voccurs during the firstoil period of the `series vofimpulsesto `be transmittedfromthe controlcnice. 'l

Upon the ,picking up of the vrelay 'VP,'ba'ck Contact 98 is open soAthat the relay -E 'is deenergized Awhich opens lfront contact |'0"|included in front contact 84 which inturn deenergizes `they relay FA.'In other. Words, the relay. FAMrepeats the line responsive relaynieansregardlesstof whetherlit Thus, it

is the relay F1 orthe relay F2 which is actuated in response to' thecorresponding frequencies placed'upon the line circuit. The reason for'this` is `because the'relaySB picks up and closes front contact I3so'that front contact .||4.of relay F2 can .control the Lrelay JFA thesame as frontcontact '814 Tof .relay FI. fIt is noted inthis connectionthat the picking up of relay` SBopens backcoutact 3i) 'and deenergizesthe line .condition .relays R and L, opening front contact ||5 of krelay.'L,

the significance of which willbe discussed here- 1 inafter. l p y YAssuming that 4the rst foff;perio.d is repeated by the relay FA, theclosure of -back contact .|04A completes a stick circuit foi-'the relayVVPLfrom j througha circuit' including front contact 45 of relay SB,front contact..|.0.3 of .relay..SC,

back contact |04 ofrelay EA, Wire .|'|'6 iront. Contact' l of relay VP,windings of relay to,

( Thus, the relay VPis maintained energized duringthe ofPperiods even'though 'its pick-up circuitis opened at 'frontcontact ||0 by thepicking up.of the flrs't step relay V1, .for

example. .i

The yiirst step `rela'y V1 is'caused to vbe picked up upon the releaseof the'relay 'FA by reason of a circuit closed from ,and including frontcontact '6| .of relay SC,"back-.contact `|V|8 of .relay FA, wire H9,front contact-|20 of relay VP, back contact |2| of relay V4, back.Contact |22 of .relay V2, windings of relay V1, to (a). `As soon as therelay V1 is picked up, its stick circuit is closed from through acircuit including front conrelay V3; front contact"|25 ofrelay V1,windings of relay V1, to

an' energizing 'circuit for relay E incll'lding front Contact 91 ofrelay V1 and front contact. 98 .of re- |01 for energizing eitherrelay T1or relay VVT2 in accordance with the character of impulse re-. quiredfor the rst `element of the code for ther station being selected. i

Disregarding for the moment the particular The picking up of thestepping relay closes4 character of the next impulse, it is impressed onthe line circuit by the picking up of either the transmitting relay T1or the transmitting relay T2, and such impulse is repeated by thecorresponding line responsive relay means F1 or F2 which in turn isrepeated by picking up of the relay FA.

The opening of back Contact |04 of relay FA opens the stick circuit forthe relay VP including the front contact I I1 of relay VP, the otherstick circuit forthe relay VP including its front contact I I2 alreadyhaving been opened at back contact I I by thepicking up of the relay V1.Thus, the relay VP drops away .in response to the second picking up ofthe relay FA.

This dropping away of the relay VP opens the energizing circuit for therelay E at front contact 98 of relay VP, which causes relay E toterminate that impulse by deenergizing the particular transmitting relayT then energized at open front contact 0I. i

The second dropping away of the relay FA a the end of the second impulseof the series closes the pick-up circuit for the stepping relay V2 fromk(-l-)fthrough a circuit including front contact 6I of the relay SC, backcontact I I8 of relay FA, wire I I9, back contact of relay VP, backconfa tact I of relay LV, back Contact |26 of relay V3, front contact|21 of relay. V1, windings of relay V2, to As soon as the relay V2 picksup, its stick circuit is closed by the closure of its front contact |28completing a stick circuit through back contact |29 of the relay V4 tothe bus wire |23, which bus wire is energized throughout the cycle ofoperation. The picking up of the stepping relay V2 prepares the relays Tfor en,- ergization and causes the relay E to be energized by closure offront contact 90. v

During the next on period of the series of impulses, the relay FA ispicked up, and causes an; other pick-up circuit to be closed for therelay VP by reason of the closure of front contact |04 of relay FAandthe closure of front contact |69 of the relay V2. c This picking upof the relay VP causes the relay E to be again deenergized to terminatethat impulse. v During the following oi period of the series of impulsesas repeated by the relay FA, the closure of back contact I8 completes apick-up circuit for the relay V3 from (-1-) ,through a circuit includingfront contact 6I of relay SC, back contact II8 of relay FA, wire II9,front contact |20 of relay VP, back contact I 2| vof relay V4, frontcontact |22 of relay V2, windings of relay vV3, to v As soon as therelay V3 `picks up, it closes front contact |30 to complete a stickcircuit through contact I3I of relay LV to the bus |23. The picking upof relay W opens back contact |24 included in the stick circuit of therelay V1 so that such relay V1 drops away, its function i'or thisparticular cycle of operation having been completed.` From the abovedescription of the operation of the stepping bank up to the point of thepicking` up of the relay V3, it will be seen that the half-` step relayVP assumesopposite positions on alternate impulse periods while thesuccessivel stepping relays V pick up on the successive o periodsY ofthe series of/impulses. This stepping operation continues until the laststepping relay LV is `picked up to end the cycle of operation as willlater be described. It is of course understood that the number ofstepping relays is commensurate with the number of controlsandindications necessary to be transmitted in actual practice.

It will be noted that the last stepping relay LV and the next to thelast is maintained energized until. relay SB drops at the end of thecontrol cycle.

It will also be noted that each of the other stepping relays is droppedaway upon picking up of the second succeeding stepping relay in thesteppingvrelay bank.` This serves the purpose that the stepping relaysare not using energy for a longer period than necessary and also reducesthe amount of current that needs to be broken at any one time upon thedropping away of a stepping relay which wouldbe of a substantial valueif/all of the stepping relays were maintained until the end of theoperating cycle.

FREQUENCY SELECTION FOR CONTROL Cones When controls are to betransmitted from the control oice, the iield stations are selected oneat a time in accordance with the combination of thedifferent frequenciesused for the impulses applied to the line circuit for a portion of thecomplete code, while the remaining impulses have frequencies selected inaccordance with the controls to be transmitted to the selected station.In brief, a complete control code comprises a station selecting code andthe controls for theselected station.'

' As above mentioned, each impulse applied to the line circuit causesthe stepping means at the control oice and the field stations to takeone stepl irrespective of 'the particular frequency of such impulse.l f

In accordance with the present invention, each impulse may be either oftwo frequencies, and the number of diierent combinations of impulses forthe station selecting portion of the vcontrol code depends upon thenumber of impulses used. The dilerent frequencies are arranged incombina.-k tions in accordance with lthat code principle which providesthat when two diierent frequencies are employed two diierentVcombinations of code calls are obtained for one step; four different fcombinationsy of impulses for two steps; eight combinations for fourdifferent steps; sixteen combinations for four steps; thirty-twodilierent combinations 'for ve steps; and so on, each additional steporimpulse doubling the number of possible code calls. In the presentdisclosure, only three steps have been shown, and although any number ofsteps may be employed, it is believed that this number is sucient for anunderstanding of the present invention, and a typical code rtable isgiven below.v

Typical code table Number of station code call' Step 1 Step 2 Step 3 1f1 f1 f1 fl fl f2 l 2 l .il ff', f2 a i f i t il t f2 fz f1 Y fr fa fzWith a code call assigned .to each field station selections are madebetween half of the total number of stations on the rst stationselecting step in accordance with the frequency of the im.- pulse forthat step; and similarly on the second station selectingstep, selectionis made between half of the stations remaining after the rst selection,the particular half depending upon the frequency of the second impulse.This selection field stations.

.fZ-iz feontinues .until :the fend of thelestatinn: selecting '.stepswhen:` only fone stationimans the-f selectedastation.

In: accordance with this principle of` `codeise- -,lection, the.eodeijumpersfinntheontrol oiiceI can bearrangedto assignanyneode eallxtoanyield station as mayzbe desired. Butgior-tbe sakee'of fsimplicitygmassigning kthe codes, 'it fis; probably desirablezto assign .the'codeszirrttherorderfofithe flhshas been "done forzthe .pur- .poses :of"the presentadisclosure ntoirprov'ide that lwhich .requires Athreeimpulsesl of ffrequeneyiyl (see fcodeztablefabove). :Thisiisfzeieeted:by the l ooderjumpers |35, l-eand H131; -whilei the'station ,codefcallTNO. i 2 for istation\;No.:2t ist provided .of .the frequencies "f1, f1,f2. .1However,:itrist0;be understood that any ofthe possiblecodesmightibe .assigned to'thesel stationsby :merelyishifting'sthepositions of these code jumpers. Also,r-tbis assign :ment of..codes.isifor station seleetionizforz'control .position-off theilewerLSMLitoaenereizeieithenthe relay 'IiP-:or :thefrllelay YInother Words, theaii'npulsesofthezfourthstep isof a:f1;or f2;frequencyr,depen-dingupen:whethena;normalerreyerseeon- `trol 4is :desired -fior'.the1swtch'-machine @at ythe .niieldflocation ,:Inra simila-ixmanner.Ithe difienentrfrequencies to be transmitt'edfcan beselected.ontanylnumber of station selectingsteps in accordancewith the number ofstations in thesystem; and any 1- number of :controlfgsteps can'.be-used; depending @upon the Agnurnbersof switches fand-.signals,tombe :controlled :at the fstation.

1Eim'or" CONTROLJCYCLE: AT THE 'CONTROL OFFICEAThei,application,-oftlfxelast impulse of a control eycleto the linecircuitis yterminated by the .dro-pping away of :the y.relay E rwhiehrealises the 1steppingzrelay LV to V,pickup ibut in; so :doingy no..energysisapliedto the `line circuitlbecausefthere A-cycles -ofoperation Lwhich is indepe-ndentfoffthe -c-ode` assignment for 'station.-selection for :indi-- "cation cycles -of -operationfasy Will beexplained more =in zdetail ihereinafter.

'IMBULSING OPERATION. A'LKCCJBHIROLt ,OFEIGE lAt the ybeginningioflthe`eontrolrzyele ofvoperation the initiatingfor.' eenditioningfimpulse` isprovided loyatheenergization 'of'the transmitting frelay T1 to providethat the` pulses fofithe ffrequency f1. .'As -above .pointed out,AA this-energy'rfor the relay T1 is supplied through back Aczontaetftl `of` therelay SCat the same timevthatfthe relay E is-pioke'd:up'bynitsenergizing circuit-(above pointed out. fButlWhenthefVPrelayfrespon'dsfias 'is the case asy soon as the'relayfSC picks-up),fthe rrE lrelayiisr dropped so that upon the 'pickin-g `up 'of "the4.relay SC the *continued energization 'of er the `relay "T1 'for Atheinitiating impulse Yis'lcontinued through-'front contaotfll ofthe1relay/E lwhich very shortly 'thereafter' drops away. `jThe droppingof the relay E, of course, -causes :the -rst1steppingrelay 'V1--to piekup. l

(As soon as `the-relayVlpicks unibe-circuit :forthe relays'T1 orT2-is5preparedfso*that-oneor 4the other `can' beenergizedinraccordancewith the eharacteref the code elementrequiredffor the rststep Whenithe relay El-piek-supv andcloses vits Yiront Contact m tocause-"energy` to,` be aprelayf LV. 4:Thiscessation of `the.applcationfoi `impulses'lizoftlie line circuit fis, of f'courseerepeated by the relay 1 FA which ,L in turn deenergizes y the4ArelaysirSA,@SlnandeSCsuccessively i .'Iheedrop- 'zp'ngrfofrthe relaySC'gdeenergfizesy the 'relayzgGC :atiitsfrontontaet88,-sozthat no moreenergyzoan be dapplied to :thefrelays T1.,or TZLthroughithe Wire@Seinem-*fronticontact 83 offrelayfC,

:andzthevrelaygLC'are: droppedv vbut when itl-le-step-l ping relay`V4:'isgipioked: upibfecauserthe Nback con- -ftact 9 I -foffthe -relay'Cis,v of eourse.: alreadympen sanditheveontactzzof the relay SBisalsofopen, y-`making thercontaetr-txof relay V4theflastncon- .ILC and'LGS. Asnsoonzasithe :relay :LCS :drops -away,` the front -eontact 159'is :opened conditioningithezrelay "C for :deener-gization uponvtl'lezi'release of the relay SA subsequentvto'ithef-termination ofthelast..impulsaoi.` the control,l cycle. This rs'tiek :circuituof`:the"frelay'ft'l is opened Ably-""fnoiit `contact/Hier relay 'SA' bllts:again closed by'back ',conta'eti l ofz'relayf SC.

when the last cyclefdemarking relay "SC-"becomes 'deenergiz-ed; apernssion'impulse is place'duponvthe line `eireuit'for restoring theline v"tact |5| of relay SC, backy contact"|52 of relay -ingfeithertherelay`Tl or'therelay i VFor example, tlfielrelayt I LC `is picked'upfor; the

station No. l so 'that' the `stepping` relayV1 Ycloses its 'frontContact 1Utoconnectenergyto the bus Wire ldd. which supplies`energytlfrrouglfi--ront` which through uPfront contaoti M9 'effrrelayflLC' R.="b-ack'contactf |53'of vrelayC,r-to"tlf1elous Wire4"16,:'vyiriciirifzs of relay'TZ; to

*The resulting Aapplication of animplulse Voffrequency f2 causes theline responsive relay `means fF2- toibe Eenergized fat VVthe 'control'Iofce and*v at -ea'ch of 'the' eld stations. ""I'hiskenergizationwofrelay F2 at i th control Voffice f does,l not energize VtheyrelayF-A,.loeoause front contact?! |"3 of Arelay ASB is yopen fas Wellas the 'fronteontact ||15.of

the line eonditionrelay L, However,y the closure 4scribed.ibut therelay/"L ldoes not ypickup until this permission impulse is fterrinated."The length fof this permission nulseis fdeterrnin'edby the jpickupperiod, vof, the relay flRcin 'the cont-rol "oice 'which is madeslow-acting lfonthevv purpose of timingjthis'impulse. i

2Att-er atimetherelay R picksgupfte'openi back dropping' "the `relay "T2which', off course. is repeated by the line responsive relay means Fzinthe foontrol oflice and 7fforrevspondiner relays at each-fof'theoeldstations. "If'he'opening'offfront contact 33 of relay F2 then allows therelay L to pick up so as to close front contact II to .permit the relayFA to be responsive to any initiating impulse originating at a leldlocation. This will be appreciated by again noting that the initiatingpulses from the iield locations are of the frequency f2 While theinitiating impulse from the control office is of the frequency f1.

OPERATION AT FIELD STATIONS The reception of a conditioning impulse offrequency f1 at each of the iield stations causes the line responsiverelay means to repeat such impulse and effect certain conditioningoperations at each of the eld stations which can be typically consideredin connection with the eld station No. 1 disclosed in Figs. 4A and 4B.

More specifically, the picking up of the relay IFl closes front ContactI5@ for energizing the line repeating relay IFA through an obviouscircuit. front contact I55 to energize the relay ISA, which in turncloses its contact |56 to energize the relay ISB. As soon as the relayISB picks up, it opens back contact 34, deenergizing the lineconditioning relays IR and IL to prevent any initiation of an indicationcycle from the eld station as will be described in detail hereinafter.As soon as the relay ISA picks up it closes front contact |58 while thepicking up of relay ISB closes contact |59. Both of these contacts |58and |59 are in multiple for completing the pickup circuit for the relayIFA as controlled by contact |60 of relay IF2. This is necessary tomaintain relay IFA controllable by relay IF2 inasmuch as the droppingaway of the relay IL opens contact I6I which is not again closed untilthe end of a permission impulse, as will be described inconnection withthe end of the control cycle at the field station.

The reception of the conditioning impulse at the field locations alsocloses 'a pick-up circuit for the station selecting relay SO at each'and every station so that any station is available for its selection inaccordance with the particular code received. For example, the pick-upcircuit for the relays 'ISO and ISOS is closed from (-1-) through acircuit including back contact |62 of relay ISB, front contact |63 ofrelay IFl, back contact |64 of relay IFZ, Wire I65, back Contact |66 ofrelay IV4, back contact ISB of relay IV3, back contact |69 vof relayIV2, back contact |10 of relay IV2, winding of relay I SOS, Winding ofrelay ISO, to

It is noted that this pick-up circuit for the relays ISO and ISOS isclosed uponfthe reception of the -conditioning impulseonly until theyrelay ISB is picked up at which time an immediate shift-over is made tohold the relay ISO through stick circuits. More specifically, the relayISOS is provided with a stick circuit from through circuit includingfront contact I1I of relay ISB, front contact I12 of relay IFA, wire|13, front contact |14 of relay ISOS, lower winding of relay ISOS, to

With the relay ISOS thus maintained energized, a holding stick circuitis also closed for the relay ISO from (-1-), through a circuit includingfront contact I1I of relay ISB, wire |15.

front contact I 16 of relay ISOS, front contact- |11 of relay ISO,lofwer winding of relay ISO, to ).Y

As soon as the relay ISB picks upA during the vconditioning period, -apick-up circuit 'is closed The line repeating relay lIlA closes its '5bILV, back contact |61 of relay 300 `which completes a shunt circuit forthe contact 293 of relay IFA until the stepping relay IV1 is picked upat Iwhich time the 'front contact 30| 'of relay IVP completes a stickcir-cuit including back contact 293 of relay IFA which will beunderstood by analogy to the circuits described for the relay VP in thecontrol olice.

With the relay IVP picked up during the conditioning period, togetherlwith the picked-up condition of the station selecting relay ISO, thestepping bank is prepared to pick up the stepping relay IV1 upon thefirst 01T period following the conditioning period.

More specically, as soon as the relay IFA is released, a pick-up circuitis closed for relay IVI from through `a circuit including front contact34 of relay ISB, back contact 302 of relay IFA, wire 303, front contact304l of relay ISO. front contact 305 of relay IVP, ba-ck contact 306 ofrelay IV4, back contact 301 of relay IV2, windings offrelay IVl, to Assoon as the relay I V1 picks up a stick circuit is closed from (-I),through a circuit including front contact 308 of relay ISB, wire 309,back contact 3| 0 of relay IV3, front contact 3II of relay IV1, windingofrelay |V1, to

It is believed to be unnecessary to'point out in detail the operation ofthe stepping bank at the field station, inasmuch as the operation ofsuch stepping bank can be readily understood by analogy to the detailoperation given with respect to the stepping bank in the 'control cnice.However, it should be noted that the circuit 'for the stepping relaysIVat the field station include front contact 304 of the relay ISO, sothat if such relay drops away at any point in a control cycle ofoperation, vthe stepping operation is immediately stopped. A similarfunctioning of the system occurs during an indication cycle of operationbecause at such time the front Contact 3|2 of relay ISI is lincluded inthe stepping circuit, and such relay ISI drops out Whenever the stationfails t-o be selected for transmitting indications. When the steppingrelays V at any station fail to follow the impulses on the line circuitbecause of the dropping of the corresponding relay SO or SI, the relayVP also ceases its operation.

The stepping operation at the eld station may be briey summarized bystating that the halfstep relay IVP is causedto assume an oppositeposition on alternate impulse periods; while a stepping relay IV ispicked up during each succeeding off period so long as a stationcontinues to be selected.

STATION SELEcTroN pulses fo-rming a part of the station selection code,the station selecting relay SO for each station is selectivelymaintained energized or is deenergized dependent upon whether thecharacter of the impulse for such impulse period corre-

